Rhizopus arrhizus

Rhizopus arrhizus belongs to the kingdom Fungi, phylum Zygomycota, and genus Rhizopus. It is a widely distributed saprophytic fungus that can act as a facultative parasite under favorable conditions. This pathogen is a primary cause of rapid soft rot in a variety of agricultural crops, both in the field and during post-harvest storage.

The fungus affects a broad range of hosts, including vegetable crops like tomatoes and peppers, fruits such as strawberries and peaches, and industrial crops like sunflowers. Typical symptoms include sudden tissue softening followed by the appearance of a thick, grey-to-black, fuzzy mycelial growth covering the affected area, often leading to total fruit collapse.

The development cycle of Rhizopus arrhizus involves both asexual reproduction via sporangiospores and sexual reproduction via zygospores. These spores are wind-dispersed and can also be spread by water or insect vectors. The fungus can persist in the soil and on crop debris for extended periods, serving as a constant source of primary inoculum for subsequent planting seasons.

The fungus thrives in warm and humid conditions, with optimal development occurring between +25°C and +35°C and relative humidity exceeding 85%. These conditions are critical for spore germination and mycelial penetration. Infection is frequently facilitated by wounds or mechanical damage on the surface of the fruit or vegetable, which allows the pathogen to bypass natural physical barriers.

Economic damage caused by this pathogen is significant due to the rapid destruction of produce quality. Losses can escalate quickly in storage facilities if sanitation is poor. Control strategies focus on an integrated approach, including minimizing mechanical damage during harvest, implementing strict sanitation protocols in storage, maintaining proper ventilation, and using appropriate pre-harvest fungicide applications.